1. Field of the Invention
The present invention relates to an intake system for an internal combustion engine, and, more particularly, to an intake system improved by utilizing resonance effects of intake air.
2. Description of Related Art
A known internal combustion engine has been developed with improved charging efficiency obtained by utilizing resonance effects of intake air. Typically, an intake system for supercharging by utilizing the resonance effects of intake air is used for an internal combustion engine which has a plurality of cylinders divided into two groups, the cylinders in each group being disposed so that adjoining cylinders in each cylinder group do not fire one after another. Individual, or discrete, intake passages of the cylinders of each cylinder group are joined together at their upper ends by a conflux chamber, such as a surge tank. The surge tank is connected to what is called a collection intake passage, i.e., a resonant passage, with a pressure reverse portion formed at a desired location of the resonant passage.
In a tuned speed range of the engine, fundamental pressure waves of intake air, generated at intake ports of the cylinders of each cylinder group, and reflected pressure waves, reversed at the pressure reverse portion, coincide with one another in phase so as to cause the pressure waves of intake air, propagating both ways between the pressure reverse portion and each cylinder, to resonate in the resonance passage. In such a way, a resonant pressure wave having a high amplitude is generated by means of the resonance of intake air due to pressure vibrations generated individually in the cylinders. The resonant pressure wave thus obtained forces the intake air to be charged into a combustion chamber of each cylinder with high charging efficiency. Such an intake system is known from, for instance, Japanese Unexamined Patent Publication No. 62-159725.
In the prior art intake system which has elongated conflux tanks, such as surge tanks, for the respective groups of cylinders, if the surge tanks are interconnected at their intermediate longitudinal portions by a communication passage and the communication passage is controlled to open in a range of higher engine speeds, the resonance effect of intake air is abolished and the generation of troughs of engine output torque accompanying the resonance effect can be diminished.